This invention relates to an apparatus for processing X-ray image data by means of a linear differential filter.
In accordance with a method adopted in a conventional X-ray image data processing apparatus, two X-ray images, e.g., a mask image and a contrast image, of an object such as a patient are subjected to a digital subtraction, and contrast variation between X-ray image data in a digital form, or varied components of contrast of X-ray image data which is obtained by the administration of an X-ray contrast medium into a blood vessel of the patient are extracted, whereby an angiographic image thus obtained is provided as diagnosis data.
However, according to this method, since two X-ray images are merely subjected to the digital subtraction, deterioration of the S/N ratio occurs.
In such a conventional X-ray image data processing apparatus, another method may be adopted. According to this method, a plurality of mask image data is calculated to provide averaged mask image data. Then, a plurality of contrast image data is similarly calculated to provide averaged contrast image data. The thus obtained averaged values of the mask and contrast image data are subjected to the subtraction to provide desired subtraction image data. The subtraction image data obtained by the latter method results in an improved S/N ratio as compared to the former method. However, such an averaging method may result in the loss of specific data on diseased portions of a patient which is necessary for correct diagnosis.
The present invention has been made in consideration of this and is based on the fact that a digital subtraction is essentially to execute differentiation of a plurality of X-ray image data taken at various sampling instants, and to extract the pixels whose contrast variations are great. An object of the present invention is to provide an X-ray image data processing apparatus which is capable of providing useful diagnosis data with an improved S/N ratio without resulting in the loss of specific data on the diseased portions of the patient which is necessary for correct diagnosis.